#define _GNU_SOURCE
#include <sys/types.h>
#include <ucontext.h>
#include <pthread.h>
#include <signal.h>
#include <stdio.h>

static void hello(void)
{
	printf("hello, signal\n");
}

static void trampoline(void)
{
	printf("trampoline\n");
}

static void sigsegv_handler(int sig, siginfo_t *si, void *ctx)
{
	ucontext_t *uc = ctx;
	unsigned long prev_rip;
	unsigned long *rsp;

	prev_rip	= uc->uc_mcontext.gregs[REG_RIP];

	rsp		= (void *) uc->uc_mcontext.gregs[REG_RSP];

	*(--rsp)	= (unsigned long) hello;

	printf("rsp=%p, ctx=%p\n", rsp, ctx);

	uc->uc_mcontext.gregs[REG_RSP]		= (unsigned long) rsp;
	uc->uc_mcontext.gregs[REG_RIP]		= (unsigned long) trampoline;
}

void touch_stack(void)
{
	char array[4096];
	int i;

	for (i = 0; i < sizeof(array); i++) {
		array[i] = 0xff;
	}

	printf("%p\n", array+i);
}

static void make_kill(void)
{
	char use_some_stack[8];

	use_some_stack[0] = 0xff;

	if (kill(0, SIGSEGV) < 0)
		perror("kill");
}

void setup(void)
{
	struct sigaction sa;

	sigemptyset(&sa.sa_mask);
	sa.sa_flags     = SA_RESTART | SA_SIGINFO;

	sa.sa_sigaction = sigsegv_handler;
	sigaction(SIGSEGV, &sa, NULL);
}

static void *start_thread(void *arg)
{
	for (;;) {
		make_kill();

		printf("main\n");

		touch_stack();
	}

	return NULL;
}

int main(int argc, char *argv[])
{
	pthread_t id;

	setup();

	if (pthread_create(&id, NULL, start_thread, NULL) != 0)
		perror("pthread_create");

	if (pthread_join(id, NULL) != 0)
		perror("pthread_join");

	return 0;
}